What is meant by gene expression?

Gene expression refers to the process through which the information encoded in a gene is used to produce a functional product, typically a protein or RNA molecule. This process involves several key steps, including transcription, where the DNA sequence of a gene is copied into messenger RNA (mRNA), and translation, where the mRNA is used as a template to build the corresponding protein. Thus, gene expression is essential for the proper functioning of cells and the manifestation of traits in organisms.

The other options do not accurately capture the full scope of gene expression. Replication of DNA pertains to the copying of genetic material rather than expressing it. The modification of proteins, while an important cellular process, occurs after a gene has been expressed and relates to post-translational modifications rather than the expression itself. Lastly, the breakdown of RNA is a different process that involves the degradation of RNA molecules, which is not involved in the synthesis of gene products.